VM not receiving data from usb-to-serial adapter

I'm using VMware, with Windows XP as guest. I can connect my MOXA USB-RS 432 adapater and see it in the guest. I use this adapter to transfer firmware into a board, using MODBUS communication. If i connect the adapter to a machine with Windows XP directly installed (without using VM) the system works. But using the VM i can send commands (tx led blinks in the MOXA) but i receive nothing.

I tried to tweak the MOXA configuration, and pretending that it's a USB-to-RS 232 adapater (instead of a USB-to-RS 432), i can see also the RX led blinking but the system isn't still working (i really can't understand this behaviour).

I heard of latency problems in VMs. I found this article: Can I use a USB-to-serial adapter to talk to my development board from VMWare Fusion?

I also tried to follow VMware support for "changing the input speed of the serial connection" (it didn't work and i don't if it's the right way). VMware support is here: https://www.vmware.com/support/ws3/doc/ws32_devices3.html#1023765

I tried everything for 3 days and now i'm stuck. Does anyone has any suggestion?